A borate and metal boride composite-coated positive electrode material and preparation method thereof

Abstract

The present invention provides a borate and metal boride composite coated positive electrode material and a preparation method thereof, belonging to the technical field of sodium ion batteries. The present invention directly mixes positive electrode particles, metal boride and non-metallic boron source to obtain a coated mixture and then calcines it in stages. The first stage of calcination: boric acid or boron oxide has a low melting point and has good fluidity after melting at low temperature, so that the metal boride can be evenly distributed on the surface of the positive electrode particles; the second stage of calcination: high temperature promotes the reaction wettability of the metal boride and the surface of the layered oxide positive electrode material, ensuring the close bonding and complete coverage of the coating layer, and slowing down the side reaction between the positive electrode material and the electrolyte. The preparation process of the present invention is simple, does not use dangerous boron hydride compounds, is simple and safe to operate, is low in cost, and is easy to mass produce. The sodium ion battery obtained by using the positive electrode material prepared by the present invention has a high specific capacity and excellent cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a borate and metal boride composite-coated positive electrode material and a preparation method thereof. Background Art

[0002] Sodium-ion batteries, with their high safety, abundant raw material sources and low cost, are expected to be first used in large-scale energy storage devices and low-speed transportation. Among them, layered transition metal oxides have a high specific capacity, making them the most promising sodium-ion battery positive electrode material for commercial production.

[0003] However, the poor storage properties of layered transition metal oxides in the air and the excess residual alkali on their surface usually cause gelation of the positive electrode slurry, and serious interfacial side reactions are prone to occur in the electrolyte, resulting in increased internal resistance of the battery, resulting in poor cycle performance and rate performance.

[0004] Surface coating is a common method for improving material performance, such as cycling and safety, and is widely used in the modification of cathode materials. Coating with metal borides and / or borates has been shown to be an effective means of improving the cycling and rate performance of cathode materials.

[0005] Chinese patent CN 114267841 A discloses a fully surface-coated high-nickel single crystal ternary material. Using a redox reaction, a reducing borohydride solution undergoes a redox reaction on the surface of the oxidizing high-nickel ternary material, generating a metal boride precursor that is evenly distributed on the surface of the substrate. After calcination, the metal boride is formed. This invention has several drawbacks: First, ethanol is typically used as a solvent for coating, which requires subsequent drying, posing a risk in industrial production. Second, the reducing borohydride (sodium borohydride, potassium borohydride, or lithium borohydride) is a highly explosive and hazardous chemical that can cause combustion and explosion when exposed to water, humid air, acids, oxidants, high heat, and open flames. Storage and handling are dangerous and inconvenient. Third, because borohydride is highly reducing and reacts with water, an inert gas (argon or nitrogen) must be introduced to remove water vapor and air from the reaction, further increasing production costs. Chinese patent CN113540466A discloses dispersing a nickel-cobalt-manganese ternary material precursor in a solvent. A divalent metal salt and sodium borohydride are then added under a protective atmosphere for reaction. After the reaction is complete, the precursor undergoes solid-liquid separation and drying, then is mixed with boric acid, ground uniformly, and calcined to produce a nickel-cobalt-manganese ternary material precursor coated with a metal boride and borate complex. This invention also utilizes borohydride, and the overall reaction process is relatively lengthy. Summary of the Invention

[0006] The object of the present invention is to provide a borate and metal boride composite-coated positive electrode material and a preparation method thereof. The preparation process of the present invention is simple, and no hazardous chemicals such as boron hydride compounds are used. In addition, the sodium ion battery obtained by using the positive electrode material prepared by the present invention has a high specific capacity and excellent cycle performance.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a positive electrode material composite-coated with borate and metal boride, comprising the following steps:

[0009] Mixing positive electrode particles, metal boride and non-metallic boron source to obtain a coating mixture; calcining the coating mixture to obtain a positive electrode material compositely coated with borate and metal boride;

[0010] The non-metallic boron source includes boron oxide and / or boric acid;

[0011] The calcination comprises: calcining at 300-500° C. for 3-5 hours, heating to 600-800° C. for calcining for 5-10 hours.

[0012] Preferably, the metal boride includes one or more of magnesium diboride, titanium diboride, zirconium diboride and aluminum diboride.

[0013] Preferably, the mass of the metal boride is 50-80% of the total mass of the metal boride and the non-metallic boron source.

[0014] Preferably, the ratio of the mass of the positive electrode particles to the total mass of the metal boride and the non-metallic boron source is 1:(0.0005-0.008).

[0015] Preferably, the calcination is carried out in an oxygen or air atmosphere.

[0016] Preferably, the chemical formula of the positive electrode particles is as shown in Formula 1: Na x Ni a Fe b Mn c M d O 2±β Formula 1;

[0017] In formula 1, x, a, b, c, d and 2±β are the molar numbers of the corresponding elements, M is Mg 2+ 、Cu 2+ 、Zn 2+ 、Al 3+ 、B 3+ 、Co 3+ 、Y 3+ 、Ti 4+ 、Zr 4+、Sn 4+ and Nb 5+ One or more combinations thereof, wherein 0.67<x≤1, a+b+c+d=1, 0≤β≤0.1.

[0018] Preferably, mixing the positive electrode particles, metal boride and non-metallic boron source comprises: first mixing the metal boride and non-metallic boron source to obtain a composite coating agent; and second mixing the composite coating agent with the positive electrode particles to obtain a coating mixture.

[0019] Preferably, the first mixing is performed at a rotation speed of 150 to 300 rpm and for a time of 0.5 to 1 h.

[0020] Preferably, the heating rate during the calcination process is 2-5°C / min.

[0021] The present invention provides a positive electrode material compositely coated with borate and metal boride prepared by the preparation method described in the above scheme.

[0022] The present invention provides a preparation method of a positive electrode material compositely coated with borate and metal boride, comprising the following steps: mixing positive electrode particles, metal boride and a non-metallic boron source to obtain a coated mixture; calcining the coated mixture to obtain a positive electrode material compositely coated with borate and metal boride, wherein the non-metallic boron source comprises boron oxide and / or boric acid; and calcining comprises: calcining at 300-500° C. for 3-5 hours, heating to 600-800° C. for calcining for 5-10 hours.

[0023] The present invention directly mixes positive electrode particles, metal borides, and non-metallic boron sources to obtain a coated mixture, which is then calcined in stages. The first stage of calcination (calcination at 300-500°C for 3-5 hours) involves boric acid or boron oxide having a low melting point and good fluidity after melting at low temperatures, allowing the metal boride to be evenly distributed on the surface of the positive electrode particles. The second stage of calcination (calcination at 600-800°C for 5-10 hours) involves high temperature promoting the wettability of the metal boride and the surface of the layered oxide positive electrode material, ensuring close bonding and complete coverage of the coating layer, and slowing down side reactions between the positive electrode material and the electrolyte. After calcination, the boric acid or boron oxide reacts with the residual alkali sodium carbonate / sodium hydroxide on the surface of the positive electrode particles, enters the lattice oxygen on the surface of the material, and generates interfacial polyanion borate, forming a positive electrode material coated with borate and metal boride. The preparation process of the present invention is simple, does not use dangerous boron hydride compounds, is simple and safe to operate, is low-cost, and is easy to mass-produce.

[0024] In addition, the borate and metal boride composite coated positive electrode material prepared by the present invention has the following advantages: boric acid or boron oxide can react with the residual alkali on the surface of the positive electrode particles, reduce the surface alkalinity, and effectively improve the cycle performance and air stability of the positive electrode material. Metal borides have high chemical stability, high thermal conductivity and high electrical conductivity as superconductor materials. The high electrical conductivity of metal borides can enhance the electrical conductivity between materials, and their high chemical stability plays a physical isolation role to avoid corrosion by the electrolyte. The reaction wettability of metal borides with the surface of layered oxide positive electrode particles can not only completely cover the surface of the secondary particles, but also penetrate into the primary particles, ensuring the close bonding of the coating layer, which is beneficial to structural stability. In addition to boric acid and boron oxide reacting with the surface oxygen of the positive electrode particles, metal borides also have oxygen affinity and can react slightly with the surface oxygen of the positive electrode particles to form a bond, effectively stabilizing the surface oxygen of the positive electrode material and inhibiting the precipitation of lattice oxygen. The combination of borates and metal borides can be synergistically dispersed on the surface of the positive electrode material, solving the problem of residual alkali on the surface of the material and reducing hygroscopicity, while improving the electronic conductivity of the positive electrode material. It can also inhibit side reactions with the electrolyte, reduce gas production, and improve the cycle stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope test image of the material obtained in Example 1 of the present invention;

[0026] Figure 2 This is a scanning electron microscope test image of the material obtained in Example 2 of the present invention;

[0027] Figure 3 This is a scanning electron microscope test image of the material obtained in Example 3 of the present invention;

[0028] Figure 4 This is a scanning electron microscope test image of the material obtained in Example 4 of the present invention;

[0029] Figure 5 This is a charge and discharge curve diagram of the sodium ion battery provided in Example 1 of the present invention;

[0030] Figure 6 This is a charge and discharge curve diagram of the sodium ion battery provided in Example 2 of the present invention;

[0031] Figure 7 This is a charge and discharge curve diagram of the sodium ion battery provided in Example 3 of the present invention;

[0032] Figure 8 This is a charge and discharge curve diagram of the sodium ion battery provided in Example 4 of the present invention;

[0033] Figure 9 This is a charge and discharge curve diagram of the sodium ion battery provided in Comparative Example 1 of the present invention;

[0034] Figure 10 This is a charge and discharge curve diagram of the sodium ion battery provided in Comparative Example 2 of the present invention;

[0035] Figure 11 This is a charge and discharge curve diagram of the sodium ion battery provided in Comparative Example 3 of the present invention;

[0036] Figure 12 This is a charge and discharge curve diagram of the sodium ion battery provided in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0037] The present invention provides a method for preparing a positive electrode material composite-coated with borate and metal boride, comprising the following steps:

[0038] Mixing positive electrode particles, metal boride and non-metallic boron source to obtain a coating mixture; calcining the coating mixture to obtain a positive electrode material compositely coated with borate and metal boride;

[0039] The non-metallic boron source includes boron oxide and / or boric acid;

[0040] The calcination comprises: calcining at 300-500° C. for 3-5 hours, heating to 600-800° C. for calcining for 5-10 hours.

[0041] In the present invention, unless otherwise specified, all raw materials used are commercially available products well known in the art.

[0042] The present invention mixes positive electrode particles, metal boride and non-metallic boron source to obtain a coating mixture.

[0043] In the present invention, the chemical formula of the positive electrode particles is preferably as shown in Formula 1:

[0044] Na x Ni a Fe b Mn c M d O 2±β Formula 1; In Formula 1, x, a, b, c, d and 2±β are the molar numbers of the corresponding elements, and M is preferably Mg 2+ 、Cu 2+ 、Zn 2+ 、Al 3+ 、B 3+ 、Co 3+ 、Y 3+ 、Ti 4+ 、Zr 4+ 、Sn 4+ and Nb 5+One or more combinations thereof, wherein 0.67<x≤1, a+b+c+d=1, 0≤β≤0.1.

[0045] In the present invention, the positive electrode particles are preferably prepared by methods well known in the art, specifically referring to the preparation method of sodium-rich layered oxide materials disclosed in CN115663173A. In an embodiment of the present invention, the chemical formula of the positive electrode particles is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is prepared by the following method: Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 were dry mixed in a high-speed mixer according to the molar ratio of Na / Me=1.05. The dry mixed materials were heated to 500℃ at a heating rate of 4℃ / min in an air atmosphere and kept warm for 5h. Then, the temperature was raised to 900℃ at a heating rate of 2℃ / min and kept warm for 13h. After the sintering was completed, the sintered materials were cooled, crushed and sieved in turn to obtain the positive electrode particles NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2. Me is the total molar amount of all metal elements including Ni, Fe, Mn and M.

[0046] In the present invention, mixing the positive electrode particles, metal boride and non-metallic boron source preferably includes: first mixing the metal boride and non-metallic boron source to obtain a composite coating agent; and second mixing the composite coating agent with the positive electrode particles to obtain a coating mixture.

[0047] In the present invention, the first mixing is preferably performed in a high-speed mixer, the rotation speed of the first mixing is preferably 150 to 300 rpm, and the time is preferably 0.5 to 1 hour.

[0048] The present invention has no special requirements for the second mixing process, as long as the positive electrode particles and the composite coating agent can be mixed evenly.

[0049] After obtaining the coating mixture, the present invention calcines the coating mixture to obtain a positive electrode material compositely coated with borate and metal boride.

[0050] In the present invention, the calcination includes: calcining at 300-500°C for 3-5 hours (first stage calcination), heating to 600-800°C for 5-10 hours (second stage calcination); preferably, calcining at 350-450°C for 3.5-4.5 hours, and heating to 650-750°C for 6-8 hours. In the present invention, the heating rate during the calcination process is preferably 2-5°C / min.

[0051] The first stage of calcination: Boric acid or boron oxide has a low melting point and has good fluidity after melting at low temperature, so that the metal boride can be evenly distributed on the surface of the positive electrode particles; the second stage of calcination: High temperature promotes the reaction wettability of the metal boride and the surface of the layered oxide positive electrode material, ensuring the close bonding and complete coverage of the coating layer, and slowing down the side reaction between the positive electrode material and the electrolyte.

[0052] In addition, after calcination, boric acid and / or boron oxide react with the residual alkali sodium carbonate / sodium hydroxide on the surface of the positive electrode particles, enter the lattice oxygen on the surface of the material, and generate interfacial polyanion borate, forming a positive electrode material coated with borate and metal boride.

[0053] After the calcination is completed, the present invention preferably cools, crushes and sieves the obtained calcined material in sequence to obtain a positive electrode material compositely coated with borate and metal boride.

[0054] The preparation process of the invention is simple, no dangerous boron hydride compounds are used, the operation is simple and safe, the cost is low, and large-scale production is easy.

[0055] The present invention provides a positive electrode material compositely coated with borate and metal boride prepared by the preparation method described in the above scheme.

[0056] The positive electrode material coated with the borate and metal boride composite has the following advantages: boric acid or boron oxide can react with the residual alkali on the surface of the positive electrode particles to reduce the surface alkalinity, effectively improving the cycle performance and air stability of the positive electrode material. Metal borides have high chemical stability, high thermal conductivity and high electrical conductivity as superconductor materials. The high electrical conductivity of metal borides can enhance the electrical conductivity between materials, and their high chemical stability plays a physical isolation role to avoid corrosion by the electrolyte. The reaction wettability of metal borides with the surface of layered oxide positive electrode particles can not only completely cover the surface of the secondary particles, but also penetrate into the primary particles, ensuring the close bonding of the coating layer, which is beneficial to structural stability. In addition to the reaction of boric acid and boron oxide with the surface oxygen of the positive electrode particles, metal borides also have oxygen affinity and can react slightly with the surface oxygen of the positive electrode particles to form a bond, effectively stabilizing the surface oxygen of the positive electrode material and inhibiting the precipitation of lattice oxygen. The combination of borates and metal borides can be synergistically dispersed on the surface of the positive electrode material, solving the problem of residual alkali on the surface of the material and reducing hygroscopicity, while improving the electronic conductivity of the positive electrode material. It can also inhibit side reactions with the electrolyte, reduce gas production, and improve the cycle stability of the material.

[0057] The borate and metal boride composite coated positive electrode material and its preparation method provided by the present invention are described in detail below with reference to the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0058] Example 1

[0059] Preparation of positive electrode material coated with 0.1wt% (H3BO3:MgB2=0.5:0.5)

[0060] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and Na2CO3 were dry mixed in a high-speed mixer according to the molar ratio of Na / Me=1.05. The dry mixed materials were heated to 500℃ at a heating rate of 4℃ / min in an air atmosphere and kept warm for 5h. Then, the temperature was raised to 900℃ at a heating rate of 2℃ / min and kept warm for 13h. After the sintering was completed, the sintered materials were cooled, crushed and sieved in turn to obtain the positive electrode particles NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2;

[0061] (2) Boric acid and metal boride MgB2 were mixed in a high-speed mixer at a mass ratio of 0.5:0.5 at a mixing speed of 200 rpm for 0.5 h to obtain a composite coating agent;

[0062] (3) The positive electrode particles and the composite coating agent were mixed in a mass ratio of 1:0.001. The mixed material was heated to 350°C at a heating rate of 3°C / min in an air atmosphere and kept warm for calcination for 5 h. The temperature was then increased to 700°C at a heating rate of 2°C / min and kept warm for calcination for 10 h. After the calcination, the calcined material was cooled, crushed and sieved in turn to obtain the composite coated positive electrode material.

[0063] Example 2

[0064] Preparation of positive electrode material coated with 0.25wt% (H3BO3:MgB2=0.4:0.6)

[0065] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the mass ratio of boric acid to metal boride MgB2 is 0.7:0.3, and in step (3), the positive electrode particles and the composite coating agent are mixed in a mass ratio of 1:0.0025. The remaining steps are consistent with embodiment 1.

[0066] Example 3

[0067] Preparation of positive electrode material coated with 0.1wt% (H3BO3:AlB2=0.5:0.5)

[0068] The difference between this embodiment and embodiment 1 is that the metal boride in step (2) of this embodiment is AlB2. The remaining steps are consistent with embodiment 1.

[0069] Example 4

[0070] Preparation of positive electrode material coated with 0.1wt% (H3BO3:ZrB2=0.5:0.5)

[0071] The difference between this embodiment and embodiment 1 is that the metal boride in step (2) of this embodiment is ZrB2. The remaining steps are consistent with embodiment 1.

[0072] Comparative Example 1

[0073] This comparative example provides a positive electrode material, the positive electrode material chemical formula is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The difference between this comparative example and Example 1 is that step (2) and step (3) are not performed, and only step (1) is performed.

[0074] Comparative Example 2

[0075] Preparation of positive electrode material coated with 0.05wt% H3BO3

[0076] The difference between this comparative example and Example 1 is that step (2) is not performed in this comparative example. In step (3), the positive electrode particles and H3BO3 are mixed in a mass ratio of 1:0.0005, and the mixed material is heated to 350°C in an air atmosphere at a heating rate of 3°C / min and kept warm for 5 hours. The sintered material is then cooled, crushed and sieved in sequence to obtain a positive electrode material coated with 0.05wt% H3BO3.

[0077] Comparative Example 3

[0078] Preparation of positive electrode material coated with 0.05wt% MgB2

[0079] The difference between this comparative example and Example 1 is that step (2) is not performed in this comparative example. In step (3), the positive electrode particles and MgB2 are mixed in a mass ratio of 1:0.0005. The remaining preparation methods and parameters are the same as those in Example 1.

[0080] Comparative Example 4

[0081] Preparation of positive electrode material coated with 0.05wt% ZrB2

[0082] The difference between this comparative example and Example 1 is that step (2) is not performed in this comparative example. In step (3), the positive electrode particles and ZrB2 are mixed in a mass ratio of 1:0.0005. The remaining preparation methods and parameters are the same as those in Example 1.

[0083] Structure and performance characterization:

[0084] The morphology of the prepared composite coated cathode material was analyzed by field emission scanning electron microscopy (SEM) (Tescan MIRALMS, Czech Republic). The SEM images of the composite coated cathode materials prepared in Example 1, Example 2, Example 3 and Example 4 are shown in FIG. Figure 1 、 Figure 2 、 Figure 3 and Figure 4 As shown in FIG. 1 , FIG. 2 , FIG. 3 , and FIG. 4 , the positive electrode material primary particles prepared were uniformly distributed with dot-shaped coatings. In Example 2, the coating amount was increased from 0.1 wt % to 0.25 wt %. The ratio of metal boride in the composite coating agent (0.6) was relatively high, resulting in a large and dense amount of coatings on the positive electrode material primary particles.

[0085] Furthermore, the residual alkali content on the surface of the material was tested using potentiometric titration. The test results are shown in Table 1.

[0086] Table 1 Residual alkali content on the surface of composite coated positive electrode materials of Examples 1 to 4 and Comparative Examples 1 to 4

[0087]

[0088]

[0089] As can be seen from Table 1, compared to the high residual alkali content in Comparative Example 1, boric acid coating treatment in Examples 1-4 and Comparative Example 2 helps reduce residual alkali on the material surface, thereby improving cycle performance. Comparative Examples 3 and 4, which were treated with only metal borides, only showed a slight decrease in residual alkali.

[0090] Electrical performance test:

[0091] In a dry room with a dew point below -40°C, the prepared composite coated positive electrode material, binder, and conductive carbon black were mixed in NMP (N-methylpyrrolidone) at a mass ratio of 90:5:5, homogenized, and the solid content was controlled at 45%. The mixture was coated on an aluminum foil current collector, vacuum-baked at 110°C for 5 hours, pressed into shape, and then punched into a sodium positive electrode sheet. Button-type half-cells were assembled in an argon-filled glove box. The counter electrode was a metal sodium sheet, the separator was PE, and the electrolyte was 1 mol / L NaPF6 in EC / DMC (Vol 1:1). The button-type cells were subjected to charge and discharge tests. The button-type cell testing equipment was the commercial LAND battery testing system of Wuhan Landian Electronics Co., Ltd.

[0092] The battery was charged and discharged at 2.0-4.0V and 0.1C rate. Figures 5 to 12 The first charge and discharge test curves of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 2. For specific test results, see Table 2.

[0093] Table 2 Electrical properties of Examples 1 to 4 and Comparative Examples 1 to 4

[0094] First cycle charge capacity (mA / g) First cycle discharge capacity (mA / g) First effect (%) Example 1 148.9 145.0 97.37 Example 2 146.6 139.6 95.26 Example 3 146.7 142.0 96.78 Example 4 146.0 142.1 97.35 Comparative Example 1 148.8 142.4 95.69 Comparative Example 2 147.5 142.5 96.61 Comparative Example 3 146.8 141.5 96.42 Comparative Example 4 146.8 141.2 96.23

[0095] As can be seen from Table 2, except for Example 2, the first efficiency of the positive electrode materials prepared in the other examples and comparative examples of the present invention is improved after coating compared with that of the comparative example 1. The first-cycle discharge specific capacity of Example 1 is also higher than that of the comparative example 1, indicating that the appropriate coating amount and coating type are helpful to improve the first efficiency and the discharge capacity.

[0096] The battery was cycled 30 times at 2.0-4.0 V and 1 C rate for cycle performance testing. See Table 3 for specific test results.

[0097] Table 3 Cyclic performance of Examples 1 to 4 and Comparative Examples 1 to 4

[0098]

[0099] As can be seen from Table 3, after 30 cycles, the discharge capacity of Example 1 is still maintained at 114.7 mAh / g, and the capacity retention rate is 86.81%. In contrast, the uncoated positive electrode material prepared in Comparative Example 1 has only 106.3 mAh / g left, and the capacity retention rate is 81.61%, which is closely related to the irreversible phase change behavior during the cycle. Comparative Example 2, Comparative Example 3, and Comparative Example 4 are only coated with boric acid or metal boride, and the cycle performance is slightly improved. The data in Table 3 proves that the long cycle performance of the composite coated sodium ion battery layered positive electrode material prepared by the present invention is significantly better than that of the unmodified or single-coated sodium ion battery layered positive electrode material, and the preparation method effectively improves the cycle performance of the positive electrode material.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material composite-coated with borate and metal boride, characterized in that: The following steps are involved: Mixing positive electrode particles, metal boride and non-metallic boron source to obtain a coating mixture; calcining the coating mixture to obtain a positive electrode material compositely coated with borate and metal boride; The non-metallic boron source includes boron oxide and / or boric acid; The calcination comprises: calcining at 300-500° C. for 3-5 hours, heating to 600-800° C. for calcining for 5-10 hours; The mass of the metal boride is 50% of the total mass of the metal boride and the non-metallic boron source; The ratio of the mass of the positive electrode particles to the total mass of the metal boride and the non-metallic boron source is 1:0.001; The chemical formula of the positive electrode particles is shown in Formula 1: Na x Ni a Fe b Mn c M d O 2±β Formula 1; In formula 1, x, a, b, c, d and 2±β are the molar numbers of the corresponding elements, M is Mg 2+ 、Cu 2+ 、Zn 2+ 、Al 3+ 、B 3+ 、Co 3+ 、Y 3+ 、Ti 4+ 、Zr 4+ 、Sn 4+ and Nb 5+ One or more combinations thereof, wherein 0.67<x≤1, a+b+c+d=1, 0≤β≤0.

1.

2. The preparation method according to claim 1, characterized in that The metal boride includes one or more of magnesium diboride, titanium diboride, zirconium diboride and aluminum diboride.

3. The preparation method according to claim 1, characterized in that The calcination is performed under an oxygen or air atmosphere.

4. The preparation method according to claim 1 or 2, characterized in that Mixing the positive electrode particles, the metal boride and the non-metallic boron source includes: first mixing the metal boride and the non-metallic boron source to obtain a composite coating agent; and second mixing the composite coating agent with the positive electrode particles to obtain a coating mixture.

5. The preparation method according to claim 4, characterized in that The first mixing has a rotation speed of 150 to 300 rpm and a time of 0.5 to 1 hour.

6. The preparation method according to claim 1 or 3, characterized in that The heating rate during the calcination process is 2-5°C / min.

7. A positive electrode material composite-coated with borate and metal boride prepared by the preparation method according to any one of claims 1 to 6.

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